1. Technical Field of the Invention
The present invention relates generally to radio frequency (RF) power amplifiers and, more particularly, to CMOS, FET, SOS and/or SOI power amplifiers that provide linear and non-linear amplification capability from the same PA.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems include national and/or international cellular telephone systems, the Internet, and point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards or protocols. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), wideband CDMA (WCDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), radio frequency identification (RFID), Enhanced Data rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS), and extensions and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a mobile or cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, as well as others, communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of RF carriers of the wireless communication system or a particular RF frequency for some systems) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other network.
For each wireless device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to an antenna and includes a low noise amplifier, one or more signal conversion stage(s) and a data recovery stage. The transmitter includes a data processing stage, one or more frequency conversion stage(s) that may include a modulator, and a power amplifier. The power amplifier amplifies the RF signal prior to transmission via an antenna.
One of the key stages for transmission is the power amplifier (PA). PAs provide the necessary power amplification for transmitting the RF signal. The power provided by the PA typically depends on the particular wireless communication technology employed, the standard or protocol being utilized and the distance and/or medium that the transmitted signal traverses to an intended receiving device. For example, Bluetooth™ devices transmit at lower power than cell phones, because the distance between Bluetooth™ wireless communication is much shorter than the distance between a cell phone and a base station, such as a cell phone tower. Thus, the size of a PA, which relates directly to its power generation capability, depends on the power required for transmission.
Furthermore, PAs are designed or configured to operate either in a linear mode or a non-linear mode. Linear PAs are widely used to transmit varying amplitude signals, such as OFDM (Orthogonal Frequency-Division Multiplexing), 8PSK (8 Phase Shift Keying), etc., in which the PA operates in class A, A/B, C, E, F etc. Linear PAs generally provide linear amplification of an input signal, but with reduced efficiency. Alternatively, non-linear PAs operate in class B, C, D or E to provide non-linear amplification, but with better power efficiency.
In constructing a PA, the PA is typically designed to provide power amplification for a particular purpose and the ability to provide a certain amount of transmitted power. For example, an integrated circuit that contains a PA may be selected for a mobile device (e.g. cell phone) based on the standard or protocol used for wireless communication and the linear or non-linear operation of the PA may be dictated by the specifications of the standard or protocol. If linear operation is to be practiced, the PA is designed accordingly. Similarly, if non-linear operation is to be practiced, the PA is designed accordingly.
In some instances, a device may support two different communication protocols that require the PA to switch between linear and non-linear modes of operation. For example, GSM uses a constant amplitude modulation, so that a non-linear PA may be employed to provide upwards of 45% efficiency. However, when the same PA is utilized for EDGE/WCDMA, which uses phase and amplitude modulation, the PA is backed off into a linear range. This transition of the operating mode of the PA may reduce the efficiency to around 20%, or even less. Because the PA is typically the single largest consumer of current and PAs are usually optimized for the higher power mode, this reduction in efficiency results in significant waste of power. Generally, prior art practice has been to accept this power loss in efficiency at low-power linear amplification.
Therefore, a need exists for a PA to provide both linear and non-linear amplification capability and in which better PA efficiency is obtained when operating in the linear mode.